The wheel bearing devices having the following structures have been developed: a structure called first-generation structure in which double-row roller bearings are independently used; a second-generation structure in which a vehicle-body attachment flange is integrally provided to an outer member, the second-generation structure having evolved from the first-generation structure; further, a third-generation structure in which an inner rolling surface of one of the double-row roller bearings is formed integrally with an outer periphery of a hub wheel integrally having a wheel attachment flange; and still further, a fourth-generation structure in which a constant velocity universal joint is integrated with the hub wheel and an inner rolling surface of another of the double-row roller bearings is also formed integrally with an outer periphery of an outer joint member constituting the constant velocity universal joint.
It is necessary to press-fit the wheel bearing device having the first-generation structure into a knuckle on a vehicle body side, and hence the number of man-hours is required for assembly and replacement. However, the wheel bearing device having the first-generation structure can be manufactured at lower cost than the wheel bearing devices having the second-generation and third-generation structures, and hence the wheel bearing device having the first-generation structure is mainly used for light automobiles and small automobiles in many cases.
As illustrated in FIG. 21, the wheel bearing device having the structure called first generation (for example, Patent Literature 1) includes the following: a hub wheel 102 having a flange 101 extending in a radially outer direction; a constant velocity universal joint 104 having an outer joint member 103 engaged with the hub wheel 102; and a bearing 100 arranged on an outer peripheral side of the hub wheel 102.
The constant velocity universal joint 104 includes the outer joint member 103, an inner joint member (not shown) arranged in the outer joint member 103, balls (not shown) arranged between the inner joint member and the outer joint member 103, and a cage (not shown) which retains the balls. The outer joint member 103 is constituted by a cup-shaped mouth section 107 in which the inner joint member is housed, and a stem shaft 123 projected from the mouth section 107.
Further, the hub wheel 102 includes a barrel section 113 and the flange 101. A larger-diameter first portion 115a and a smaller-diameter second portion 115b are formed on an outer end surface 114 (end surface on a side opposite to the joint) of the flange 101. A brake rotor 140 is externally fitted onto the first portion 115a, and a wheel (not shown) is externally fitted onto the second portion 115b. 
As illustrated in FIG. 22, the bearing 100 includes the following: an outer race 105 having double-row outer rolling surfaces 120 and 121 formed on an inner periphery thereof; a pair of inner races 108 and 109 having inner rolling surfaces 118 and 119 formed on outer peripheries thereof, the inner rolling surfaces 118 and 119 being opposed to the outer rolling surfaces; and double-row rolling elements 122 rollably housed between the outer rolling surfaces 120 and 121 of the outer race 105 and the inner rolling surfaces 118 and 119 of the inner races 108 and 109. Then, as illustrated in FIG. 21, a cutout portion 116 is provided on an outer peripheral surface of the barrel section 113 of the hub wheel 102, and the inner races 108 and 109 are fitted to the cutout portion 116. Further, a bolt insertion hole 112 is provided in the flange 101 of the hub wheel 102. A hub bolt 141 for fixing the wheel and the brake rotor 140 to the flange 101 is inserted into the bolt insertion hole 112.
A stem shaft 123 of the outer joint member 103 is inserted into the barrel section 113 of the hub wheel 102. In the stem shaft 123, a screw portion 124 is formed in an end portion thereof on a side opposite to the mouth section. A spline portion 125 is formed between the screw section 124 and the mouth section 107. Further, another spline portion 126 is formed on an inner peripheral surface (radially inner surface) of the barrel section 113 of the hub wheel 102. When the stem shaft 123 is inserted into the barrel section 113 of the hub wheel 102, the spline portion 125 on the stem shaft 123 side and the spline portion 126 on the hub wheel 102 side are engaged with each other.
A nut member 127 is screwed into the screw section 124 of the stem shaft 123 protruding from the barrel section 113, and the hub wheel 102 and the outer joint member 103 are coupled to each other. In this case, an inner end surface (back surface) 128 of the nut member 127 and an outer end surface 129 of the barrel section 113 are brought into contact with each other, and a back surface 130 of the mouth section 107 and an end surface 131 of the inner race 109 are brought into contact with each other. That is, when the nut member 127 is tightened, the hub wheel 102 is sandwiched by the nut member 127 and the mouth section 107 through intermediation of the inner races 108 and 109. In this case, under the state in which a cutout end surface 132 of the hub wheel 102 and an end surface 133 of the inner race 108 are brought into contact with each other, and in which the back surface 130 of the mouth section 107 and the end surface 131 of the inner race 109 are brought into contact with each other, hitting surfaces 135 and 136 of the inner races 108 and 109 are hit against each other. In this case, a radially outer surface of the outer race 105 serves as a fitting surface 105a, and is press-fitted into a radially inner surface 145a of a knuckle 145 on a vehicle body side.
Generally, the inner races 108 and 109, the outer race 105, and the rolling elements (steel balls) 122 are formed of high-carbon chrome bearing steel such as SUJ2 or a material equivalent thereto. Further, those members are hardened by immersion quenching or the like so as to have the hardness of from 58 to 64 HRC as a whole. Note that, HRC represents Rockwell Hardness C-Scale.
Incidentally, the outer race 105 is formed by trimming a raw material as a short cylindrical body. However, as a shape of the outer race 105, it is necessary to form rolling surfaces, seal fitting portions (seal mounting surfaces), and the like in a radially inner surface thereof, which leads to increases in weight of the material to be removed (material loss, which is equal to a difference of a weight of the product from a weight of the charged material) and in material cost corresponding thereto.
Under the circumstances, in recent years, there have been proposed outer races formed by a rolling process which enable material cost reduction. In this case, first, a blank is formed by hot forging or the like. The blank has a rough shape and a diameter smaller than that of a completed outer race. Next, the diameter of the blank is increased by cold rolling, hot rolling, or the like. After that, the blank is processed by a latching process into a product shape in which a grinding margin is left. Then, thermal hardening treatment is performed to the core of the blank, and grinding is performed thereon. Blanks are completed in this manner.
Regarding the cases of forming blanks, there have been a case where only an outer race is subjected to hot forging, and a case of so-called “two-stage removal” in which an outer race and one inner race are simultaneously forged and separated from each other at a last step of the forging steps (Patent Literature 2). Further, examples of the methods of forming blanks by cold rolling include various ones (Patent Literatures 3, 4, 5, and 6, for example).
Generally, cold rolling processes are performed with a cold rolling machine as illustrated in FIG. 24. The cold rolling machine includes a mandrel 150 for a radially inner surface and a forming roll 151 for a radially outer surface. On an outer peripheral surface of the mandrel 150, there is an outer-race-radially-inner-surface forming section 152 which forms the radially inner surface of the outer race 105. On a radially outer surface of the forming roll 151, there is formed an outer-race-radially-outer-surface forming section 153 which forms the radially outer surface of the outer race 105.
The outer-race-radially-inner-surface forming section 152 includes rolling-surface forming portions 152a and 152a and seal-fitting-portion forming portions 152b and 152b. Further, the outer-race-radially-outer-surface forming section 153 includes an annular-recessed-portion forming portion 153a and fitting surface forming portions 153b and 153b. 
In this case, a blank 160 is constituted by a short cylindrical body having basically straight inner and outer diameters as illustrated in FIG. 23. As illustrated in FIG. 24, under a state in which the blank 160 is externally fitted to the mandrel 150 and in which the blank 160 is sandwiched by the mandrel 150 and the forming roll 153, the forming roll 153 is rotated about an axial center thereof. In this manner, the outer race 105 having a shape as illustrated in FIG. 25 can be formed.
Note that, in the outer race 105 illustrated in FIG. 25, an annular recessed portion 155 is provided at an axial center portion of a radially outer surface (knuckle press-fitting surface) 105a. Due to formation of the annular recessed portion 155, a protruding portion 156 swelling to a radially inner side is provided on a radially inner surface 105b of the outer race 105. Then, rolling surfaces 120 and 121 are formed on both sides of the protruding portion 156.
Further, in order to achieve weight reduction and cost reduction, there have been proposed bearings (double-row angular bearings) in which inner and outer races are formed by a pressing process (Patent Literature 7).
That is, as illustrated in FIG. 26, the double-row angular bearing disclosed in Patent Literature 7 includes the following: an outer race 173 formed of a pressed steel plate and having double-row raceways 171 and 172; a plurality of inner races 176 and 177 having raceways 174 and 175 corresponding to the double-row raceways 171 and 172 of the outer race 173, respectively; and double-row rolling elements 178 arranged between the double-row raceways 171 and 172 of the outer race 173 and the raceways 174 and 175 of the inner races 176 and 177. The outer race 173 of this roller bearing is internally fitted to a housing 180 and fixed thereto.
Further, a recessed portion 161 is formed at a part corresponding to a gap between the double-row raceways 171 and 172 on an outer peripheral surface of the outer race 173. An elastic body 162 for elastically urging the outer race 173 and the housing 180 is interposed between the recessed portion 161 and the housing 180. The inner races 176 and 177 are externally fitted to a shaft (not shown) through intermediation of an annular spacer 163. Note that, the annular spacer 163 is provided for preventing the inner races 176 and 177 from being disarranged in an axial direction.    Patent Literature 1: JP 2007-120771 A    Patent Literature 2: JP Hei 05-66215 B    Patent Literature 3: Japanese Utility Model Application Laid-open No. Sho 62-63419    Patent Literature 4: JP Hei 03-90239 A    Patent Literature 5: JP 2539751 B    Patent Literature 6: JP 2006-181638 A    Patent Literature 7: JP 2004-245260 A